C3 Quantitative chemistry

• How do you work out percentage mass of an element in a compound

  Ar x number of atoms of that element

  ----------------------------------------------- x 100 = perc mass

  Mr of the compounds
• What is one mole?

  One mole of a substance is an amount of that substance that contains 6.02x10^23 particles
• How do you work out number of moles?

  Moles = mass / Mr

  (Mr mole lives under a mass triangle)
• When does a reaction stop?

  When all of one of the reactants is used up

  Any remaining reactants are in excess
• What is the reactant that is fully used up called?

  The limiting reactant
• What is the amount of product formed directly proportional to?

  The limiting reactant
• In terms of gases, what is true at any temperature and pressure?

  At any temp and pressure, equal numbers of moles of any gas will occupy the same volume
• At room temp and pressure (20C and 1 atm) one mole of gas occupies?

  24dm^3
• How can you measure concentration in g/dm^3?

  Conc = mass of solute / volume of solvent

  (can never triangle)
• How can you measure concentration in mol / dm^3?

  Conc = number of moles of solute / volume of solvent
• What is atom economy?

  It tells you how much of the mass of the reactants is wasted when manufacturing a chemical and how much ends up as useful product (efficiency of reaction)

  
  

  Atom economy = Mr of desired products / Mr of all reactants x 100
• Is high or low atom economy better and what for?

  High atom economy is better for profits and the environment
• What is yield?

  Yield is the amount of product you get
• What is percentage yield? What do 0% and 100% signify?

  Percentage yield = mass of product actually made (g) / max theoretical mass of product (g) x 100

  
  

  100% means all the product you expect was obtained

  0% means no reactants were converted into products
• What are the 3 reasons why 100% yield is unattainable?

  1. Not all the reactants react to make products

  2. There may be side reactions

  3. You lose some product when you separate it from the reaction mixture
• Reaction pathways with high atom economy are useful for what?

  Small cost

  Less waste
• 4 factors that reduce percentage yield?

  Incomplete reactions

  Chemicals stick to apparatus

  Separation difficulties

  Side reactions
• What does atom economy measure?

  Measures amount of reactant that ends up as useful product
• Solution of conc (g/dm^3) = ..?

  Solution of conc (g/dm^3) = Mass of substance (g) / vol (dm^3)
• What is a solute? What do you need to calculate it?

  A substance that is dissolved in a solution

  Can be calculated if you know the conc of the solution

  Volume of solution
• What do you need to calculate the conc of a solution?

  -Volume of 2 solutions that react completely

  -Conc of one of the solutions
• At room temp and pressure, 1 mole of gas occupies how much volume?

  24dm^3
• What is a solvent? What is a solution?

  1. A solvent is the liquid in which a solute dissolves

  2. A solution is the mixture formed when a solute has dissolved in a solvent
• How to go from grams - moles and moles - grams?

  1. Mass/mr

  2. Mr x Moles
• What is the equation for the volume of a gas?

  Vol (dm^3) = moles x 24